No abstract

Progeny of Dermacentor andersoni Stiles adults collected from one "montane" and two "prairie" sites in southern Alberta, Canada, were exposed to combinations of 9:15, 11:13 and 13:11 (L:D) daily photoperiods during various stages of their life cycle. Time required for developmental and reproductive events was recorded. Significant differences in mean molting times of fed larvae were observed, yet the differences were small, and mean times were not attributed to photoperiodic regime. Fed nymphal "prairie" ticks had significantly longer developmental rates under decreasing light regimes than in constant or increasing regimes, while "montane" ticks showed no differential response to any of these regimes. Engorged "montane" females in all regimes weighed significantly more than those in either "prairie" strain, and "prairie" strain females in increasing and constant short-day regimes were significantly heavier than those in decreasing and constant long-day regimes. Photoperiod is unimportant in the regulation of fed-larval development, and the magnitude of female engorgement may be nominally favored by short-day and increasing regimes. The differential phenotypic expression of photoperiodic regulation of fed nymphal development in this tick may have resulted from selective pressures involving differences in host availability and moisture conditions in the two geographic regions.

A bimodal, diurnal rhythm of detachment was observed for engorged female Boophilus annulatus fed on Hereford heifers confined in individual stalls in an open-sided barn and exposed to ambient climate and light. In 3 experiments during which hosts were fed each morning and evening, a morning period of increased detachment activity occurred during a 6-h period centered around the 2-h collecting interval in which sunrise occurred. A 2nd peak of activity occurred during the 2-h interval that began 6-8 h later. Seventy-four to 84% of the total detachment occurred during these two 6-h intervals and most of the detachment (44-62%) occurred during the afternoon period. These experiments were done in July, September, and January when daylengths were 13 h, 27 min; 12 h, 22 min; and 10 h, 37 min, respectively. In a 4th experiment in which groups of hosts were fed at different times of the day, maximal percentages of 41.5 and 38.3 of the total detachment from morning-fed or both morning and evening-fed heifers, respectively, occurred during the 2-h interval in which the sun rose instead of during the evening. During the evening peak period, the number of engorged females that detached from these 2 groups of heifers was approximately 1/3-1/4 the number that detached during the peak period in the morning. In contrast, 43.6% of the engorged females in the evening-fed group detached during an 8-h morning period of increased detachment activity that began in the interval between 0200 and 0400 hours. About the same percentage of the ticks (38.5) detached during a 6-h period that began at 1400 hours. The less precisely delimited pattern of detachment of engorged females from cattle fed only in the evening, as contrasted with the rhythm observed for ticks that detached from heifers fed in the morning or both morning and evening, indicates that the nutritional or physiological state of the host may influence the rhythm exogenously. Whether the morning or evening peak of detachment activity is dominant is a question that remains unresolved.

Selection of lone star ticks, Amblyomma americanum (L.), that were reared in the laboratory under short-day photoperiods of 10:14 (L:D) h resulted in third generation (F3) diapause versus F3 nondiapause strain replete nymphs having significantly different mean molting times (days from detachment to ecdysis) of 100.9 versus 54.7 d, respectively; whereas, the F7 unselected laboratory control strain had an even smaller, significantly different mean molting time of 49.5 d. Two hybrid crosses of F2 nondiapause male with F2 diapause female ticks and F2 nondiapause female with F2 diapause male ticks yielded intermediate replete nymphal mean molting times of 62.0 and 68.9 d, respectively. All strains retained the ability to develop rapidly under long-day photoperiodic conditions of 14:10 (L:D) h, although F3 nondiapause strain ticks also exhibited reduced fitness, especially when exposed to the long-day stimuli. Analyses of molting times used as phenotypic values indicate that this diapause trait is incompletely dominant, and these and other observations indicate that inheritance of photoperiodically induced prolonged replete nymphal molting times is polygenic in this species.

This paper describes an inexpensive, space-saving, and labor-efficient method for housing and making repeated observations of individual ticks held under specific photoperiodic, temperature, and humidity conditions. Using 96-well assay plates to house ticks, various developmental parameters, sex, survival, etc., of several thousand individual ticks can be recorded routinely in less than 1 hr. This design also permits more than 3,500 individual ticks to be maintained in 1 small (18.9-L) aquarium that serves as a humidity chamber. A small, unilluminated constant temperature incubator was converted inexpensively into a light and temperature programmable unit to contain the aquarium by adding a timing system, light fixture, and a second thermostat.